1. Technical Field of the Invention
The present invention relates to a fuel reforming apparatus for quick starting or cold starting fuel cells wherein a fuel is reformed to a gas containing hydrogen, without needing any special equipment or utilities, and the method of starting it.
2. Description of Prior Art
Recently, research and development of fuel cell electric vehicles has been carried out positively, in particular Polymer Electrolute Fuel Cell (PEFC) with a rather low operating temperature (about 100 degrees C.) have good prospects as fuel cell. The use of methanol as a fuel is considered to be advantageous because it is easy to supply and there is no need to construct an infrastructure. For this purpose, a reformer is indispensable to convert the methanol to hydrogen.
Conventional reformers that reform methanol include, for example, the “Methanol reformer” (unexamined Japanese Patent Publication No. 50302, 1988). This reformer contains a reforming catalyst in a hollow cylindrical reaction tube, the catalyst is heated by combustion gases from burning fuel that is supplied to the outside, and the fuel gas flowing inside the tube is reformed.
However, the “Methanol reformer” specified in the unexamined Japanese Patent Publication No. 50302, 1988 presents difficulties for installing in a electric vehicle, such as (1) its large and heavy structure, (2) long starting time, (3) low response to load variations, and (4) a high concentration of CO in the hydrogen gas produced by the reformer, which attacks the electrodes of the fuel cell.
As an example of a means known in the prior art to produce hydrogen gas from methanol with a high conversion ratio, the “Method of manufacturing gas containing hydrogen” (unexamined Japanese Patent Publication Nos. 256001, 1994 and 279001, 1994) is disclosed. This method basically puts methanol, oxygen and water in contact with a heated catalyst and produces a reaction, wherein partial oxidation of the fuel takes place.
However, the “Method of manufacturing gas containing hydrogen” according to the unexamined Japanese Patent Publication No. 256001, 1994 or 279001, 1994 suffers from the problems that (5) preheating of the catalyst is time consuming and (6) although the concentration of CO can be reduced to a degree that is suitable for conventional phosphate fuel cells (about 1%), the CO concentration is still too high for application to a solid polymer fuel cell (PEFC) suitable for mounting on a car.
Another disclosure in the prior art is “Fuel reforming apparatus” (unexamined Japanese Patent Publication NO. 157201, 1996) that can produce gas containing hydrogen with an extremely low CO concentration. As shown in FIG. 1, this apparatus is composed of a reformer Re, a selective oxidation unit Sox, a partial oxidation unit Pox and a control device C; only some of the carbon monoxide is oxidized in the selective oxidation unit Sox, the rest of the carbon monoxide is oxidized in the partial oxidation unit Pox, thereby producing hydrogen gas containing a very low CO concentration (several ppm), so that the apparatus can be applied to a PEFC.
Unfortunately, the “Fuel reforming apparatus” in the unexamined Japanese Patent Publication No. 157201, 1996 has the problems of a long starting time and poor response to load variations because the apparatus is of the same indirect heating type as that described in the unexamined Japanese Patent Publication No. 50302, 1988.
In the conventional methods described above, a large amount of inert gas (for example, nitrogen gas) is heated by a heat source such as an electric heater or catalyst combuster, and is fed in through a fuel supply line, thereby heating the whole reformer. However, because of the large heat capacity of the reformer, a long time is required for the whole reformer to reach the required temperature, so when the reformer is mounted on a electric vehicle, it takes a long time to start the car from a low-temperature condition (cold start), which is a practical problem.
Another problem relevant to the aforementioned reformer is that, if a fuel gas (a gas mixture of methanol and water) is supplied when the catalyst layer of the reformer is not heated sufficiently (to a temperature at which reforming occurs), the fuel gas condenses in a low-temperature range without being reformed and moistens the catalyst, thereby deteriorating the performance of the catalyst, and the unreformed fuel gas remaining in the catalyst layer is not completely reformed before being fed to the fuel cell, and rapidly poisons the fuel cell.